A Sydney man has been jailed for more than 12 years three decades after murdering an American mathematician at a Sydney gay beat.

The jail sentence was handed down Tuesday by Justice Helen Wilson who found that in a hostile act, Scott White had punched Scott Johnson at North Head in Manly, causing the doctor to fall to his death.

“[White] did a violent act and that act is the direct cause of Dr Johnson leaving the clifftop in terror,” the judge said.

The fatal assault was done with reckless indifference to human life, with White throwing the punch near the unguarded edge of a high coastal cliff and then fleeing the scene without notifying the police after Dr Johnson disappeared over the edge.

Justice Wilson found there was not enough evidence to show that the murder was a gay hate crime, however, because White had met Dr Johnson at the Brighton Hotel and the pair had willingly gone to the gay beat together.

The outcome ends a long-running ordeal for Dr Johnson’s family who pursued justice for over three decades, refusing to believe an initial police inquest which found the death was a suicide.

White’s sentence follows an emotional NSW Supreme Court hearing on Monday where Mr Johnson’s family members described the tragedy and heartbreak that the death and following 33 years had brought.

After the hearing, brother Steve Johnson said that speaking in court was a chance to look White right in the eyes.

“I got to tell [White] what my brother was like. I got to tell him how it felt to hear that he was dead … I have to think it sunk in. He watched and listened,” he said.

An appeal of White’s conviction has already been filed after his defence team failed to overturn his guilty plea in January.

White was sentenced to 12 years and seven months in jail, and will be eligible for parole after eight years and three months.

While the initial 1989 inquest found Mr Johnson’s death was a suicide, the case was reopened in 2012.

Another inquest returned an open finding in 2012, but a third in 2017 found Mr Johnson fell from Manly’s North Head clifftops because of violence by an unidentified attacker who perceived him to be gay.

– AAP